Many devices are available to keep a beverage at a desired temperature. Some such devices include an inner portion surrounded by an outer portion with annular chamber therebetween. In U.S. Pat. No. 4,570,454, for example, a double-walled drinking vessel having a heat maintenance chamber between an inner wall and an outer wall of the vessel is disclosed. A fluid is placed between the walls, and the fluid is either heated or cooled depending upon the temperature desired for the beverage to be placed within the inner tumbler of the drinking vessel. The drinking vessel also includes an annular base in the form of a skirt that is placed around and below the bottom of the vessel. The skirt has a plurality of spaced orifices which provide for air circulation underneath the vessel, thus preventing condensation from occurring on the supporting surface. The inner tumbler and outer container are separate pieces which are suitably connected by an inner connecting annular enclosure region.
Similarly, U.S. Pat. No. 2,995,267 discloses an ice bucket having a bottom portion and a top portion. The bottom portion and the top portion are both made entirely of plastic. The bottom is shaped in a cup-like formation with a generally flattened lower surface and side walls diverging upwardly and rising to an upper peripheral free edge. The top portion has a central depression having a somewhat rounded bottom and generally cylindrical side walls. These side walls roll over or outwardly to form an upper smooth edge. From the upper smooth edge an integral skirt depends and terminates at a peripheral free edge. The skirt is angularly spaced at all points from the side wall of the depression so that a predetermined gap or air space exists between the surface walls. The upper free edge of the bottom portion is circular and has a predetermined diameter. The lower free edge of the skirt on the top is also circular and has a corresponding diameter. These diameters are the same so that the two edges may be brought together and heat sealed. The resulting product is an ice bucket in which the side wall of the bottom forms a continuation of the upper skirt and provides a uniform and continuous annular spacing from the inner depression at all points.
U.S. Pat. No. 3,189,229 also discloses a container having an enclosed annular space to keep a contained beverage at a desired temperature. The container is a pitcher which comprises a main body part, a base part and cover, each of which may be formed from a plastic. The body part includes an inner receptacle or container having a generally cylindrical wall and bottom wall and an outer casing or skirt concentric with the wall but terminating in a stepped lower edge short of the bottom wall. The bottom or base part is a one piece, cup-shaped member having short side walls. The top edge of which is stepped and a concaved bottom wall with radial downwardly extending ribs. The bottom is assembled with the body by fitting the edge onto the edge of the body and subsequently spinning the bottom by friction engagement with the ribs relative to the body to fuse the parts together. Accordingly, the bottom becomes in effect a part of the pitcher and a double wall is provided at the bottom as well as the sides of the pitcher.
Double walled containers are also disclosed in U.S. Pat. Nos. 3,804,281 and 2,526,165.
Until the present, no double-walled containers have been formed from a unitary piece of material. Two-piece assemblies such as those described above, however, are very difficult to manufacture with total success.
The normal method of assembling two-pieced, double-wailed containers is spin welding. Generally, in spin welding two components molded separately are joined by rotating one within the other, creating a melting action to fuse the two components together. That method frequently leaves an unsightly "flash" residue at the joint. Moreover, the joint usually occurs at the most undesirable position, near the top, outer edge or lip of the container. The flash must either be removed as a costly extra production step or the integrity of the weld must be compromised to reduce or eliminate the flash.
Spin welding joints are frequently incomplete. Poor welding in a two-piece design can permit contaminants to enter the annular void area between the outer and inner wails. Because the component parts cannot be disassembled, the contamination can never be removed. Distasteful odors and elevated bacteria levels may result. The danger of contamination is especially great during dishwasher cleaning.
Moreover, separate inner and outer wall components of a double-walled container are expensive to mold because each component requires a separate mold and molding machine.
It is an object of the present invention to substantially reduce or eliminate these problems associated with two-pieced, double-walled containers.
It is also desirable for a double-walled container to have a base portion to prevent formation of condensate. Prior containers of this type, disclose base portions permanently attached to the container. It is also an object of the present invention to provide a thermal container having a removable base portion.